Electrical apparatus



Oct. 7, 1941. H. F. sIvIITI-I ELECTRICAL APPARATUS Filed April 21, 1959 INVENTOR.

ATTORNEY 6.

ULHTION INSULATION INSULHTIQN Patented Oct. 7, 1941 ELECTRICAL APPARATUS Harry F. Smith, Lexington, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a

corporation of Delaware Application 'April 21, 1939, Serial No. 269;176

Claims.

This invention relates to electrical apparatus and more particularly circuit makers and breakers.

One object of this invention is to provide a circuit maker and breaker in which the closing of the circuit does not offer any resistance to movement of the contact actuating means.

Another object of this invention is to provide a circuit maker and breaker which requires very slight operating force.

A further object of this invention is to provide a circuit maker and breaker in which the change in weight of a member actuates a balance beam carrying the movable contacts.

Still another object of this invention is to provide an improved indicating means for indicating the position of the balance beam.

Another object is to provide a switch suitable for closing a plurality of circuits for operating remotely located signals or the like.

Still another object of this invention is to provide an improved moisture responsive means.

A further object of this invention is to provide an instrument which is responsive to slight changes in the relative humidity within the range of relative humidities and temperatures commonly encountered. I I

Still another object of this invention is to provide a device which requires a minimum amount of attention and adjustment in operation.

Further objects and advantages .of the present invention will; be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred form of the present invention is clearly shown.

In the drawing:

Fig. 1 is a horizontal sectional view taken on the line I-l of Fig. 2;

Fig. 2 is a vertical sectional view, with parts broken away;

Fig. 3 is a fragmentary sectional view taken on the lines 3-3 of Fig. 2;

Fig. 4 is a fragmentary view showing the details of the indicator; and

Fig. 5 is a fragmentary sectional view taken on the lines 5--5 of Fig. 2.

As shown in the drawing the circuit maker and breaker comprises a main casing -I0-which preferably is made out of molded insulating material and serves to support as well as enclose theswitch mechanism. The switch mechanism comprises a first contact element l2 and a second contact element l4, each of which is provided with a notch [6 which serves to support a balance beam [8. The balance beam l8 comprises a main bar of insulation 20 which has a first conductor 22 secured to the one side thereof and a second conductor 24 secured to the other side thereof. Each of these conductors is provided with a knife edge portion which rests in one of the notches l6 and serves to pivotally support the balance beam l8. It will be observed that the construction is such that the contact 22 is in electrical contact with the contact I2 and the contact 24 is in electrical contact with the contact M.

The conductors 22 and 24 are provided with contact fingers 23 and 25 respectively. Each con tact finger carries a section of insulation 21 at its lower extremity which terminates below the mercury contact 29 whereby the mercury level never varies. The contacts 23 and 25 move into and out of circuit making position with the mercury contact 29 placed in the glass tube 3|. The tube 3| is supported on the bracket 33a which also supports the electrical lead-in 35 which in turn is in contact with the mercury in the glass tube 3|.

As best shown in Fig. 2 a hygroscopic element generally designated by the reference character 30 is suspended from the left hand end of the balance beam l8. This hygroscopic element comprises a roll of corrugated absorbent material such as blotting paper 32 which, by virtue of the corrugations, has an extremely large surface area which is exposed to the atmosphere. The roll 32 is held in place between the spiders 33 which are held together by the pin 35. This absorbent material 32 is impregnated with a quantity of hygroscopic solution as more fully pointed out hereinafter.

In order to minimize the disturbances of the instrument by external vibration, a dash-pot arrangement has been provided which comprises a piston 36 operating within a cylinder 34 filled with a liquid, such as oil. This piston 36 is suspended from the right hand end of the balance beam I8. In order to adjust the instrument a balance nut 38 has been provided which is mounted upon the screw threaded projection 40 of the balance beam [8. The casing l 0 includes a side panel 42 which is removable so as to give access to the adjusting nut 38 as well as to the other parts of the instrument.

The general arrangement is such that as the hygroscopicv element 30 absorbs moisture the weight of the element 30 increases and this increased weight tends to unbalance the balance beam l8 with the result that a circuit is closed between the contact finger 25 and the mercury contact 29. As the moisture content of the atmosphere decreases the hygroscopic element 30 In order to induce circulation of the air through that portion of the casing in which the hygroscopic element is located, I have provided a lamp 5?! in the upper part of casing ID. This lamp is provided with a metallic shield 52 which prevents radiant heat from striking the hygroscopic element 30. The lamp supplies a sumcient amount of heat to cause circulation of air in through the opening 54 past the hygroscopic element 30 and out through the opening 55. By providing a source of heat for inducing circulation of air through the hygroscopic element 30, the instrument responds very quickly and accurately to changes in the relative humidity. The lamp 50 not only serves to set up convection currents but also serves to illuminate a transparent indicating scale 58 which is secured to the upper web member 33 by means i of a bracket 60. The transparent scale 58 has indicia placed thereon which may be observed through an opening 62 in the casing In. For purposes of illustration, these indicia have been shown as indicating the relative humidity. However, other forms of indicia may be used, such as High-Normal- Low, On-Off or any other suitable symbols. It will be observed that the opening 82 is placed opposite the lamp 50 with the result that the lamp serves to illuminate the scale 58. Another advantage of providing a heating element in the form of a lamp and providing an opening 82 adjacent the lamp is that in the event that the heating element becomes defective for any reason this fact will be readily apparent, and the necessary repairs may be made.

While it has long been recognized that a large number of materials absorb moisture in damp weather and while many instruments have been devised which make use of this fact, no one I heretofore has been able to construct a satisfactory instrument for accurately measuring the relative humidities in the lower relative humidity range, at lower temperatures. Wood is one example of a material which has long been known to absorb moisture and the expansion of wood has been used in humidity responsive instruments for a long time. It has also been proposed to use changes in various chemical compounds for measuring relative humidities. However, instruments using wood and other materials previously proposed are not satisfactory for the full relative hiunidity range normally encountered for numerous well-known reasons. Calcium chloride, for example, has also been used but is not suitable in a control of this type, because between the temperatures of about 10 F. and 80 F. and between relative humidities of about 28% and 44% it changes from the addition compound containing four molecules of water to the addition compound ocntaining six molecules of water. This change disturbs the relation between the relative humidity and the moisture absorbed by the calcium chloride with the result that the weight of the calcium chloride is not an accurate function of the relative humidity of the air within the range for which I intend my instrument to be used. Other materials which have been used have either been too corrosive, too unstable or have been otherwise unsuitable.

The most desirable form of relative humidity instrument is one which is operated in response to a change in the weight of a hygroscopic element, and I have discovered that by using a water soluble lithium salt such as lithium chloride, lithium bromide or lithium iodide it is possible to construct a humidity responsive instrument which is operable through a wide relative humidity range even at low temperatures. Glycerine, ethylene glycol, diethylene glycol, or triethylene glycol may be substituted for the lithium salt as these materials are also hygroscopic and change in weight directly in response to changes in the relative humidity throughout the desired range. Lithium chloride, for example, is suitable for use in instruments of this type since the change from lithium chloride with two molecules of water to lithium chloride with one molecule'oi water does not take place until the relative humidity has dropped below 10%. However, relative humidities below 10% are extremely rare, and therefore I am not concerned with measuring humidities below this value. Of the hygroscopic mediums which are suitable, the lithium salts are the best as they do not pick up dust and lint as readily as the others. By selecting a hygroscopic material which is stable and which changes in weight directly in proportion to the changes in the relative humidities in the relative humidity range from down to 10% and in the temperature range from 89 F. down to 10 F., it is possible to use a balance type of instrument for direct measurement of the relative humidity within this range. The materials recommended here'inabove not only have a straight line characteristic within the range for which this instrument is designed but also are very stable and otherwise suitable for use in an instrument in which the weight of the material is used for measuring the relative humidity.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1.. In a circuit maker and breaker, a main casing, a pivotally mounted contact carrying arm supported by said casing, a contact carried by said arm, a mercury cup disposed adjacent said contact, means whereby movement of said contact arm in one direction causes said contact to engage the mercury within said cup, and means for maintaining the level of mercury within said cup constant irrespective of the depth to which said contact moves into said mercury.

2. In combination, a balance beam, means for pivotally mounting said balance beam, a contact finger carried by said balance beam, a mercury contact into which said contact finger is adapted to move, means for supporting said mercury contact, and means movable out of said body of mercury as said contact finger moves into said body of mercury so as to maintain the meronly level substantially constant.

3. In an instrument adapted for measuring relative humidities as low as 10% within a temperature range. of 90 F. to 20 F. which comprises a balance beam, means for pivotally mounting said balance beam, and a hygroscopic element suspended from said balance beam so as to operate said balance beam, said element comprising a solution of lithium chloride.

1 4. In a hygroscopic instrument, a balance beam, a support for said balance beam, a weight at one end of said balance beam, a hygroscopic element supported from the other end of said balance beam, means forming a chimney around said hygroscopic element, a lamp in said chimney 10 above said hygroscopic element, a contact finger carried by said balance beam, a mercury contact into which said contact finger is adapted to 

